This invention relates to the construction of ink drop ejector components of printheads used in inkjet printing.
An inkjet printer typically includes one or more cartridges that contain ink. In some designs, the cartridge has discrete reservoirs of more than one color of ink. Each reservoir is connected via a conduit to a printhead that is mounted to the body of the cartridge. The reservoir may be carried by the cartridge or mounted in the printer and connected by a flexible conduit to the cartridge.
The printhead is controlled for ejecting minute drops of ink from the printhead to a printing medium, such as paper, that is advanced through the printer. The printhead is usually scanned across the width of the paper. The paper is advanced, between printhead scans, in a direction parallel to the length of the paper. The ejection of the drops is controlled so that the drops form recognizable images on the paper.
The ink drops are expelled through nozzles that are formed in a plate that covers most of the printhead. The nozzle plate is typically bonded atop an ink barrier layer of the printhead. That barrier layer is shaped to define ink chambers. Each chamber is in fluidic communication with and is adjacent to one or more nozzles through which ink drops are expelled from the chamber. Alternatively, the barrier layer and nozzle plate can be configured as a single member, such as a layer of polymeric material that has formed in it both the ink chambers and associated nozzles.
Ink drops are expelled from each ink chamber by a heat transducer, which typically comprises a thin-film resistor. The resistor is carried on an insulated substrate, such as a conventional silicon die upon which has been deposited an insulation layer, such as silicon dioxide. The resistor is covered with suitable passivation and cavitation-protection layers.
The resistor has conductive traces attached to it so that the resistor can be selectively driven (heated) with pulses of electrical current. The heat from the resistor is sufficient to form a vapor bubble in each ink chamber. The rapid expansion of the bubble propels a drop through the nozzle adjacent the ink chamber.
The chamber is refilled, after each drop ejection, with ink that flows into the chamber through a channel that connects with the conduit of reservoir ink. The components of the printhead (such as the heat transducer and ink chamber) for ejecting drops of ink are oftentimes referred to as drop ejectors. The action of ejecting a drop of ink is sometimes referred to as xe2x80x9cfiringxe2x80x9d the resistor or drop ejector. The ink chambers are hereafter referred to as firing chambers.
The vapor bubble that propels the drop through the nozzle rapidly collapses after each firing. This rapid collapse of the vapor bubble can, over time, damage the heat transducer as a result of cavitation. Cavitation is a vapor pocket over the heat transducer. When the ink bubble breaks, the ink forms pressure spikes that erode the resistor surface over time. As a result, the resistor may short out. To limit the effects of cavitation, firing chambers in the past have been designed with sidewalls that ensure the flow of refill ink into the chamber will be somewhat unbalanced. That is, the flow of refill ink is limited to one or two directions (as opposed to flowing uniformly over the resistor from all sides) so that the flow of refill ink moves the collapsing bubble off of the center of the heat transducer.
The type of firing chamber configurations of concern here can be generally characterized as xe2x80x9cthree-sidedxe2x80x9d firing chambers wherein the refill ink flows into the firing chamber through a single entry in the chamber. U.S. Pat. No. 4,794,410 describes such a three-sided configuration. The properties of the refill-ink flow in prior three-sided designs is such that the collapsing vapor bubble is swept from the center of the resistor and pushed against the back corners of the firing chamber as the bubble collapse completes. This configuration is useful for extending the life of the resistor by protecting the center of the heat transducer from cavitation effects. Damage to the resistor, however, can still occur since the portions of the firing chamber walls where final bubble collapse occurs is designed to be very close to the heat transducer.
The present invention is directed to a firing chamber configuration for the drop ejectors of inkjet printheads that extends the life of the heat transducer by ensuring that bubble collapse occurs at a location well spaced from the heat transducer. The sidewalls of the firing chamber are shaped relative to the firing chamber entry in a manner such that a strong jet of inflow ink is provided for moving the collapsing vapor bubble from the center of the chamber and against a curved back wall of the firing chamber.
Apparatus and methods for carrying out the invention are described in detail below. Other advantages and features of the present invention will become clear upon review of the following portions of this specification and the drawings.